1. Field of the Invention
The invention relates to a device for exposure of a peripheral area of a film circuit board provided with perforation holes, such as a TAB strip, by which unnecessary resist is exposed.
2. Description of Related Art
In a liquid crystal substrate, a portable phone, a camera, a pocket calculator, an IC card, or the like, a film circuit board is used in which an integrated circuit is deposited to an insulating film, such as a polyester film, a polyimide film or the like, with a thickness of roughly 25 to 125 microns.
FIG. 8(a) shows part of a TAB strip as one of the film circuit boards. The TAB strip TP is a strip workpiece, for example, with a width of 35 mm to 70 mm and a length of a few hundred meters, which is ordinarily wound onto a spool.
The circuit is produced on the TAB strip TP by a conductive foil (for example, a copper foil) being cemented to the above described insulating film and by the following processes and the like being repeated:
deposition process of the resist
projection printing process of the desired circuit pattern
development process of the resist
etching process in which the unnecessary conductive foil is removed. In the respective process, the film circuit board is unwound from the spool, is treated and processed, and wound back onto a spool.
The TAB strip (TP) (hereinafter also called the strip) is provided on both sides with perforation holes (PH) (also called sprocket holes) which are located at the same distance to one another (for example, with a pitch of 4.75 mm) and which are used for positioning and transport of the strip in the above described process. The strip TP is transported, for example, by rotating rollers with projections which fit into the perforation holes PH. Furthermore, in treatments such as exposure and the like, the strip TP is positioned such that the pins which are located at given positions of the device are inserted into the perforation holes PH.
As was described above, in the etching process, an unnecessary conductive foil (hereinafter also called copper (Cu) foil) is removed. When the conductive foil is not sufficiently removed, there are cases in which insulation faults and the like, and thus scrap, result. Furthermore. there is the disadvantage that the appearance is poor.
FIG. 8(b) shows a state in which a resist R has been deposited to the copper foil of the TAB strip TP. FIG. 8(b) is a cross section relative to the strip as shown in FIG. 8(a). The area shown by the double dot-dash line designates the resist R.
As was described above, the copper foil was cemented to the insulating film. On the edge of the copper foil (hereinafter also called the peripheral area), the deposited resist R protrudes as a result of the surface tension, by which the edge is thicker than the remaining area.
Conventionally, a circuit pattern is formed such a peripheral area of the copper foil is not used. The area (the area which is cross-hatched) in which a circuit pattern is formed is shown in FIG. 8(a) as the xe2x80x9ceffective pattern areaxe2x80x9d.
Conventionally, the peripheral area of the copper foil is removed in the etching process. However, since the resist R in the peripheral area of the copper foil is thick, as was described above, a greater amount of exposure is needed than in the remaining area (in the area in which the pattern is formed) in order to expose completely. With one-time exposure (exposure when the pattern is being formed), the amount of exposure is inadequate, as a result of which, in the development in the peripheral area, unexposed resist remains, and in the etching process, the copper foil is not eliminated. This unnecessarily remaining copper foil is ultimately unnecessary for attachment of the element. Thus, cutting off or the like must be performed with a cutting tool.
In order to completely expose the unnecessary resist in the peripheral area of the copper foil, it is therefore necessary to repeatedly expose only the resist in the peripheral area of the copper foil using an exposure device.
On the other hand, a process for exposing the peripheral area of a TAB strip in which only the resist in the peripheral area of the copper foil is exposed was proposed in Japanese patent disclosure document HEI 3-78237. In this publication, using FIG. 1, a process for exposure of a peripheral area is described in which UV (ultraviolet) radiation is emitted from a light source lamp through an optical fiber onto the two edges of the film and is focused by means of an exit optics unit, and in which the resist in the peripheral area of a moving film is exposed. In this process, the TAB strip is transported by a film transport device which has a friction roller and a sprocket roller. Since the TAB strip is made of a thin resin, as was described above, a serpentine is often formed during transport. The above described sprocket roller has protrusions which engage with the perforation holes of the film substrate. This prevents the film from slipping or twisting during transport.
As was described above, for the TAB strip, a copper foil is cemented to the film. But it is difficult to cement the copper foil to the film with high precision. The copper foil undulates with respect to the film roughly xc2x10.3 mm.
FIG. 9 schematically shows the above described snaking of the copper foil. FIG. 9 shows in zone (b) the case in which the copper foil is located on the position (standard position) to be cemented. FIG. 9 shows in zone (a) a case in which the copper foil is located towards the outside of the strip TP. Zone (c) of FIG. 9 shows a case in which the copper foil is located towards the inside of the strip TP relative to the standard position.
Also in the case of transport of a TAB strip TP by the sprocket roller, between the two, an amount of play of roughly 0.1 mm is required to prevent the perforation holes from colliding with the protrusions of the sprocket roller, thus being abraded and damaged. There are therefore cases in which in the TAB strip TP, a wiggle of roughly xc2x10.1 mm is formed during transport. The peripheral area of the copper foil with a maximum width of roughly xc2x10.4 mm meanders during transport through the snaking of the copper foil with respect to the TAB strip TP and through the snaking of the TAB strip TP on itself during transport.
It depends on the user who produces the film circuit boards. The region which is to be subjected to exposure of the peripheral area extends, however, from the edge of the copper foil by a width of roughly 0.3 mm (hereinafter this width is called the exposure width). The exposure width should have few faults. But the following problems must be considered:
(1) When the exposure width is less than or equal to 0.2 mm from the edge of the copper foil, it is smaller than the projecting area of the resist R, as a result of which, during development, unexposed resist remains. Therefore, an exposure width of greater than or equal to 0.2 mm is needed.
(2) The area in which the pattern is formed is fixed independently of the snaking of the copper foil as a result of the perforation holes (PH) (for example, by 1 mm to the inside from the edges of the perforation holes as shown in FIG. 9). When the copper foil is located towards the inside of the strip TP, as is shown in zone (c) of FIG. 9, the distance between the edge of the copper foil and the area in which the pattern is formed is therefore only roughly 0.4 mm. At an exposure width at least equal to 0.4 mm, the exposure light enters the area for forming the pattern and exposes the resist R which is necessary for pattern formation, resulting in possible formation of scrap.
(3) Based on (1) and (2), an exposure width of 0.3 mmxc2x10.1 mm must be ensured for exposure of the peripheral area.
U.S. Pat. No. 4,899,195 suggests a technology of exposure of a peripheral area in which exposure takes place from the edge of the workpiece with a stipulated width. Here, it is described that, using an optical detector having an emission element and a light receiving element, the position of the edge of the workpiece (wafer) is determined by changing the intensity of the light received by the light receiving element, and that, as a result of this determination signal, the irradiation position of the light for exposure of the peripheral area is controlled.
When the optical detector described in U.S. Pat. No. 4,899,195 is used to determine the edge of the copper foil Cu of the TAB strip TP, the following problem arises.
As is shown in FIG. 9, the film in the vicinity of the copper foil of the TAB strip TP is provided with perforation holes PH. The sensor light from the projection element (emission element) of the optical detector is projected onto the edge area of the copper foil (to the region in which the perforation holes PH are located). During transport of the TAB strip TP, the light receiving element receives the light transmitted by the film once and the light which has passed through the perforation holes PH once.
The light transmitted by the film is attenuated, by which the light intensity is reduced (the transmittance at a sensor light wavelength of 670 nm (nonexposure light) is roughly 20%). On the other hand, the light which had passed through the perforation holes PH is not attenuated. Here, the intensity of the light received by the light receiving element fluctuates greatly accordingly to the transport of the TAB strip TP.
Since, when the edge is determined by the optical detector in the above described U.S. Patent, the edge position is determined by the change of the intensity of the light received by the light receiving element, it cannot be distinguished whether the change of the light intensity was caused by the presence or absence of perforation holes PH or whether it was caused by the change of the edge position of the copper foil when the presence or absence of the perforation holes PH changes the intensity of the light received by the light receiving element, as was described above. Therefore, the edge position of the copper foil cannot be determined.
The invention was devised to eliminate the above described defects in the prior art. Thus, a primary object of the present invention is to devise a device for exposure of the peripheral area of a film circuit board in which the point onto which the sensor light is projected is provided with perforation holes, in which the edge of the copper foil can be exactly determined, even if the light receiving element receives the attenuated light transmitted by the film and the unattenuated light which has passed through the perforation holes, and in which the position of the irradiation area can be controlled with high precision.
In a device for exposure of the peripheral area of a film circuit board in which a film circuit board, which has perforation holes with a stipulated pitch, is transported in a certain direction, and moreover, a resist in the peripheral area of a conductive foil located in the above described film circuit board is irradiated with exposure light from a light irradiation means which has a stipulated irradiation area and in which, thus, the resist is exposed in the above described peripheral area, the above object is achieved in accordance with the invention in that an edge determination means for determining the edge area of the conductive foil located in the film circuit board is an optical detector which has a projection part and a light receiving part, that the length (irradiation length) of the sensor light which has been emitted onto the film circuit board and which has been projected by the projection part is determined in the transport direction of the film circuit board by the xe2x80x9cpitch between the perforation holes multiplied by a natural numberxe2x80x9d, furthermore, that the sensor light emitted onto the edge area of the conductive foil of the film circuit board is received by the above described light receiving part, that the above described edge determination means is subjected to motion control by a motion control means such that the amount of light reception of the above described light receiving part becomes constant, and that the area irradiated with the above described exposure light is moved in the same direction as the direction of motion of the above described edge determination means and by the same amount as the amount of motion the latter.
Since, according to the invention, the (radiation) length of the sensor light which is projected by the projection part of the optical detector and which is emitted onto the film circuit board is determined in the transport direction of the film circuit board by the xe2x80x9cpitch between the perforation holes multiplied by a natural numberxe2x80x9d, as was described above, the total amount of light received by the light reception element (the light which has passed through the perforation holes and the light transmitted by the film) does not change, regardless of the motion of the perforations according to the transport of the film circuit board. Therefore, if control is exercised in such a way that the total amount of sensor light received by the light receiving part becomes constant, regardless of the meander of the copper foil with respect to the TAB strip and regardless of the snaking of the TAB strip in itself, the resist in the peripheral area of the film circuit board can be exposed with high precision.
Furthermore, by tilting the projection parts and the light receiving part of the optical detector with respect to the film circuit board or by changing the shape of the light exit part of the projection part, the length of the sensor light in the transport direction of the film circuit board can be changed. Thus, an application can be found for exposure of the peripheral area of a film circuit board with different pitches between the perforation holes. If especially by tilting the projection part and the light receiving part of the optical detector with respect to the film circuit board, the angle thereof can be adjusted, the length of the sensor light in the transport direction of the film circuit board can be easily adjusted only by adjusting the inclination of the projection part and the light receiving part of the optical detector.
Furthermore, the area irradiated with exposure light can be moved by movement of the position of a projection lens unit which focuses the exposure light or by the movement of a mask which is located on the exit end of the exposure light. In particular, by moving the mask, it is unnecessary to move the projection lens unit. In this way, it is possible to prevent the motion control means from becoming large even if the projection lens unit becomes large and will be heavier.
Furthermore, for example, by using a parallel light linear sensor, the amount of light reception can be made more constant by means of a semiconductor laser as the optical detector when the perforation holes are moved by the transport of the film circuit board.
Since the light from a parallel light linear sensor is laser light and propagates in a straight line, the light transmitted through the film and the light which has passed through the perforation holes can be exactly recorded.
In the following, the invention is further described using several embodiments shown in the drawings.